Method of producing epitaxial silicon wafer, epitaxial silicon wafer, and method of producing solid-state image sensing device

ABSTRACT

Provided is an epitaxial silicon wafer free of epitaxial defects caused by dislocation clusters and COPs with reduced metal contamination achieved by higher gettering capability and a method of producing the epitaxial wafer. A method of producing an epitaxial silicon wafer includes a first step of irradiating a silicon wafer free of dislocation clusters and COPs with cluster ions to form a modifying layer formed from a constituent element of the cluster ions in a surface portion of the silicon wafer; and a second step of forming an epitaxial layer on the modifying layer of the silicon wafer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/946,661, filed Nov. 19, 2015, which is a division of U.S. patentapplication Ser. No. 14/078,217, filed Nov. 12, 2013 (now U.S. Pat. No.9,224,601), which claims priority to Japanese Patent Application No.2012-249221, filed Nov. 13, 2012, all of which applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method of producing an epitaxialsilicon wafer, an epitaxial silicon wafer, and a method of producing asolid-state image sensing device. The present invention relates inparticular to a method of producing an epitaxial silicon wafer free ofepitaxial defects caused by dislocation clusters and crystal originatedparticles (COPs), which method can achieve higher gettering capabilitythereby suppressing metal contamination.

BACKGROUND ART

Metal contamination is a major cause of deterioration in characteristicsof a semiconductor device. For example, for a back-illuminatedsolid-state image sensing device, metal mixed into a semiconductorepitaxial wafer to be a substrate of the device causes increased darkcurrent in the solid-state image sensing device, and results information of defects referred to as white spot defects. Recently, aback-illuminated image sensing device has been widely used for digitalcameras and mobile phones such as smartphones because it can directlyreceive light from the outside, and take sharper images or motionpictures even in a dark place and the like due to the fact that a wiringlayer and the like thereof are disposed at a lower layer than a sensorunit. Therefore, it is desirable to reduce white spot defects as much aspossible.

Mixing of metal into a wafer mainly occurs in a process of producing asemiconductor epitaxial wafer and a process of producing a solid-stateimage sensing device (device fabrication process). Metal contaminationin the former process of producing a semiconductor epitaxial wafer maybe due to heavy metal particles from components of an epitaxial growthfurnace, or heavy metal particles caused by metal corrosion of pipingmaterials of the furnace due to chlorine-based gas used in epitaxialgrowth in the furnace. In recent years, such metal contaminations havebeen reduced to some extent by replacing components of epitaxial growthfurnaces with highly corrosion resistant materials, but not to asufficient extent. On the other hand, in the latter process of producinga solid-state image sensing device, heavy metal contamination ofsemiconductor substrates would occur in process steps such as ionimplantation, diffusion, and oxidizing heat treatment in the producingprocess.

For these reasons, conventionally, heavy metal contamination ofsemiconductor epitaxial wafers has been avoided by forming, in thesemiconductor wafer, a gettering sink for trapping the metal, or using asubstrate, such as a high boron concentration substrate, having highability to trap the metal (gettering capability).

In general, a gettering sink is formed in a semiconductor wafer by anintrinsic gettering (IG) method in which oxygen precipitates (commonlycalled a silicon oxide precipitate, and also called BMD: bulk microdefect) or dislocations that are crystal defects are formed within thesemiconductor wafer, or an extrinsic gettering (EG) method in which thegettering sink is formed on the rear surface of the semiconductor wafer.

Here, a technique of forming gettering sites in a semiconductor wafer byion implantation can be given as a technique for gettering heavy metal.JP 06-338507 A (PTL 1) discloses a producing method, by which carbonions are implanted through a surface of a silicon wafer to form a carbonion implanted region, and a silicon epitaxial layer is formed on itssurface thereby obtaining a silicon epitaxial wafer. In that technique,the carbon ion implanted region functions as gettering sites.

Further, JP 2008-294245 A (PTL 2) discloses a method of forming a carbonimplanted layer by implanting carbon ions into a silicon wafer, and thenperforming heat treatment using a rapid thermal annealing (RTA)apparatus for recovering the crystallinity of the wafer which has beendisrupted by the ion implantation, thereby shortening the recovery heattreatment process.

Further, JP 2010-177233 A (PTL 3) discloses a method of producing anepitaxial wafer, comprising the steps of ion-implanting at least one ofboron, carbon, aluminum, arsenic, and antimony at a dose in the range of5×10¹⁴ atoms/cm² to 1×10¹⁶ atoms/cm² into a single crystal silicon ingotsubstrate; then cleaning the single crystal silicon ingot substratesubjected to the ion implantation, without recovery heat treatment; andthen forming an epitaxial layer at a temperature of 1100° C. or moreusing a single wafer processing epitaxial apparatus.

In addition to such formation of a gettering sink, it is important toensure high quality of a substrate per se of a semiconductor epitaxialwafer. In this respect, JP 11-147786 A (PTL 4) discloses a technique ofproducing a silicon single crystal wafer having extremely low defectdensity over the entire surface of the crystal by Czochralski process(CZ method).

CITATION LIST Patent Literature

-   PTL 1:JP 06-338507 A-   PTL 2:JP 2008-294245 A-   PTL 3:JP 2010-177233 A-   PTL 4:JP 11-147786 A

SUMMARY OF INVENTION Technical Problem

In the techniques described in PTL 1, PTL 2, and PTL 3, monomer ions(single ions) are implanted into a silicon wafer before forming anepitaxial layer. However, according to studies made by the inventor ofthe present invention, it was found that white spot defects cannot besufficiently reduced in solid-state image sensing devices produced usingsilicon epitaxial wafers subjected to monomer-ion implantation, and suchepitaxial silicon wafers are required to achieve stronger getteringcapability.

Further, in terms of producing a high quality semiconductor device, itis important that no defects are found in an epitaxial layer of anepitaxial silicon wafer to be a substrate. When dislocation clusters orCOPs are formed in a surface layer part of a silicon wafer to be asubstrate of an epitaxial silicon wafer, epitaxial defects such asstacking faults would occur due to them.

In view of the above problems, an object of the present invention is toprovide an epitaxial silicon wafer free of epitaxial defects caused bydislocation clusters and COPs with reduced metal contamination achievedby higher gettering capability and a method of producing the epitaxialwafer.

Solution to Problem

According to further studies made by the inventor of the presentinvention, irradiation of a silicon wafer with cluster ions isadvantageous in the following points as compared with implantation ofmonomer ions into the silicon wafer. Specifically, even if irradiationwith cluster ions is performed at an acceleration voltage equivalent tothe case of monomer ion implantation, the energy per one atom or onemolecule applied to the irradiated silicon wafer is advantageously lowerthan in the case of monomer ion implantation, and irradiation with aplurality of atoms can be performed at a time. This results in higherpeak concentration in the depth direction profile of the irradiatingelement, and allows the peak position to approach the surface of thesilicon wafer. Thus, the gettering capability was found to be improved.It was also found that use of a silicon wafer free of dislocationclusters and COPs as the substrate of an epitaxial wafer allows forobtaining an epitaxial silicon wafer free of epitaxial defects caused bydislocation clusters and COPs. Thus, the present invention wascompleted.

Specifically, a method of producing an epitaxial silicon wafer of thepresent invention includes a first step of irradiating a silicon waferfree of dislocation clusters and COPs with cluster ions to form amodifying layer formed from a constituent element of the cluster ions ina surface portion of the silicon wafer; and a second step of forming anepitaxial silicon layer on the modifying layer of the silicon wafer.

Here, the cluster ions preferably contain carbon as a constituentelement, and more preferably contain at least two kinds of elementsincluding carbon as constituent elements.

In the present invention, after the first step, the silicon wafer can betransferred into an epitaxial growth apparatus to be subjected to thesecond step without heat treating the silicon wafer for recovering itscrystallinity.

Further, in the first step, the silicon wafer can be irradiated with thecluster ions such that the peak of a concentration profile of theconstituent element in the depth direction of the modifying layer liesat a depth within 150 nm from the surface of the silicon wafer.

Moreover, the first step is preferably performed under the conditions ofacceleration voltage per one carbon atom: 50 keV/atom or less, clustersize: 100 or less, and carbon dose: 1×10¹⁶ atoms/cm² or less. Further,the first step is more preferably performed under the conditions of:acceleration voltage per one carbon atom: 40 keV/atom or less, clustersize: 60 or less, and carbon dose: 5×10¹⁵ atoms/cm² or less.

A semiconductor epitaxial wafer of the present invention includes asilicon wafer free of dislocation clusters and COPs; a modifying layerformed from a certain element in a surface portion of the silicon wafer;and an epitaxial layer on the modifying layer. The half width of aconcentration profile of the certain element in the depth direction ofthe modifying layer is 100 nm or less.

Further, the peak of the concentration profile in the modifying layerpreferably lies at a depth within 150 nm from the surface of the siliconwafer. The peak concentration of the concentration profile of themodifying layer is preferably 1×10¹⁵ atoms/cm³ or more.

Here, the certain element preferably includes carbon. More preferably,the certain element includes at least two kinds of elements includingcarbon.

For a method of producing a solid-state image sensing device accordingto the present invention, a solid-state image sensing device is formedon the epitaxial layer, located in the surface portion of the epitaxialwafer fabricated by the above producing method or the above epitaxialsilicon wafer.

Advantageous Effect of Invention

According to the method of producing an epitaxial silicon wafer of thepresent invention, a silicon wafer free of dislocation clusters and COPsis irradiated with cluster ions to form a modifying layer made of aconstituent element of the cluster ions in a surface portion of thesilicon wafer, thereby producing an epitaxial silicon wafer free ofepitaxial defects caused by dislocation clusters and COPs with reducedmetal contamination achieved by higher gettering capability of themodifying layer.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B, and 1C are schematic cross-sectional views illustrating amethod of producing an epitaxial silicon wafer 100 of the presentinvention.

FIG. 2 is a diagram showing the relationship between the ratio of thepulling speed to the temperature gradient at the solid-liquid interfaceand crystalline regions forming a single crystal silicon ingot.

FIG. 3A is a schematic view illustrating an irradiation mechanism of theirradiation with cluster ions, and FIG. 3B is a schematic viewillustrating an implantation mechanism of the implantation of monomerions.

FIG. 4 is a diagram showing a single crystal production apparatus usedin Examples.

FIG. 5 is a diagram showing a defect profile on a vertical section of asingle crystal silicon ingot obtained in an experiment of changing thepulling speed in Examples.

FIG. 6 is a graph showing profiles of carbon concentration with respectto the depth from the surface of a silicon wafer between InventionExample 3 and Comparative Example 3.

FIGS. 7A and 7B are graphs for comparing the capability of Ni getteringin Invention Example 3 and Comparative Example 3.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below in detailwith reference to the drawings. In principle, the same components aredenoted by the same reference numeral, and the description will not berepeated. In FIG. 1C, an epitaxial layer 20 is exaggerated with respectto a silicon wafer 10 in thickness for the sake of explanation, so thethickness ratio does not conform to the actual ratio.

As shown in FIGS. 1A to 1C, a method of producing an epitaxial siliconwafer 100 according to the present invention includes a first step ofirradiating a silicon wafer 10 with cluster ions 16 to form a modifyinglayer 18 formed from a constituent element of the cluster ions 16 in asurface portion 10A of the silicon wafer 10 (FIGS. 1A and 1B); and asecond step of forming an epitaxial layer 20 on the modifying layer 18of the silicon wafer 10 (FIG. 1C). FIG. 1C is a schematiccross-sectional view of the epitaxial silicon wafer 100 obtained by theproduction method.

First, a silicon wafer free of dislocation clusters and COPs is used asthe silicon wafer 10 in the present invention. One of the typicalexamples of a method of producing a single crystal silicon ingot that isa material of the silicon wafer 10 is the Czochralski process. Inproducing a single crystal silicon ingot using the Czochralski process,a single crystalline silicon melt is supplied into a quartz crucible,the seed crystal is pulled upward while rotating the quartz crucible andthe seed crystal, and thus a single crystal silicon ingot is growndownward from the seed crystal.

It is known that various types of grown-in defects occur in thus grownsingle crystal silicon ingots, which defects affect the devicefabrication process. Typical examples of the grown-in defects includedislocation clusters that are formed in a region where interstitialsilicon is predominant due to the growth under the condition of lowpulling speed (hereinafter also referred to as “I region”) and COPs thatare formed in a region where vacancies are predominant due to the growthunder the condition of high pulling speed (hereinafter referred to as “Vregion”). Further, in the vicinity of the interface between the I regionand the V region, defects are formed in a ring shape, which defects arecalled oxidation induced stacking faults (OSF).

The distribution of these defects in a grown single crystal siliconingot is known to depend on two factors, that is, the crystal pullingspeed V and the temperature gradient G at the solid-liquid interface.FIG. 2 is a diagram showing the relationship between the ratio of thepulling speed V to the temperature gradient G at the solid-liquidinterface (V/G) and crystalline regions forming a single crystal siliconingot. As shown in the diagram, in the single crystal silicon ingot, aCOP formation region 41 which is a crystalline region where COPs aredetected is predominant when the V/G is high, whereas an OSF latentnucleus region 42 which appears as a ring-shaped OSF region whenperforming a certain oxidation heat treatment is formed when the V/G islow. COPs are not detected in this OSF region 42. Further, the siliconwafer collected from the single crystal silicon ingot grown under acondition of high pulling speed, the COP formation region 41 mostlyoccupies the wafer, so that COPs are formed in almost the entire area inthe crystal diameter direction.

Further, an oxygen precipitation promoted region (hereinafter alsoreferred to as “Pv(1) region”) 43, which is a crystalline region whereoxygen is likely to precipitate and COPs are not detected, is formedinside the OSF latent nucleus region 42.

With the V/G being lowered, an oxygen precipitation promoted region(hereinafter also referred to as “Pv(2) region”) 44, which is acrystalline region where oxygen precipitates are present and COPs arenot detected, is formed outside the OSF latent nucleus region 42.

With the V/G being further lowered, an oxygen precipitation inhibitedregion (hereinafter also referred to as “Pi region”) 45, which is acrystalline region where oxygen is unlikely to precipitate and COPs arenot detected is formed, and a region 46, which is a crystalline regionwhere dislocation clusters are detected, is formed.

For a silicon wafer collected from a single crystal silicon ingot havingsuch a distribution of defects depending on the pulling speed, thecrystalline region other than the COP formation region 41 and thedislocation cluster region 46 is a crystalline region generally regardedas a denuded zone having no defects. The silicon wafer collected from asingle crystal silicon ingot including these crystalline regions is asilicon wafer free of dislocation clusters and COPs. Accordingly, in thepresent invention, a silicon wafer collected from a single crystalsilicon ingot made of any one of the crystalline regions other than theCOP formation region 41 and the dislocation cluster region 46, namely,the OSF latent nucleus region 42, the Pv(1) region 43, the Pv(2) region44, and the oxygen precipitation inhibited region (Pi region) 45, or acombination of them, is used as the substrate of an epitaxial siliconwafer (namely, silicon wafer 10).

Here, a “silicon wafer free of COPs” in the present invention refers toa silicon wafer having no COPs detected by the observation andevaluation described below. Specifically, first, a silicon wafer cut outof a single crystal silicon ingot grown by the Czochralski process issubjected to SC-1 cleaning (that is, a cleaning using a mixed solutionobtained by mixing ammonium hydroxide, a hydrogen peroxide solution, andultrapure water at a ratio of 1:1:15), and after the cleaning thesurface of the silicon wafer is observed and evaluated using SurfscanSP2 manufactured by KLA-Tencor Corporation as a surface defectinspection apparatus, thereby identifying light point defects (LPDs)estimated as surface pits. On this occasion, the observation mode isoblique mode (oblique incidence mode), and the surface pits are examinedbased on the ratio of the sizes measured using wide/narrow channels.Whether the thus identified LPDs are COPs or not is evaluated using anatomic force microscope (AFM). A silicon wafer in which no COPs areobserved by this observation and evaluation is referred to as a “COPfree silicon wafer”.

Note that since the detection limit size reported by the manufacturer ofthe SP2 is 37 nm, the COP free silicon wafer does not negate thepresence of COPs smaller than the detection limit size. As is evidentfrom examples described below, epitaxial defects were not observed inepitaxial silicon wafers produced using a silicon wafer in which no COPswere detected by the above observation and evaluation. Accordingly, interms of preventing the formation of epitaxial defects, if COPs are notdetected by SP2 and AFM, it is safe to consider that they do notsubstantially exist. Therefore, a silicon wafer specified by the abovedefinition is herein referred to as a “COP free silicon wafer”.

Meanwhile, dislocation clusters are defects (dislocation loops) having alarge size (about 10 μm) formed as aggregates of excessive interstitialsilicon. Whether the dislocation clusters exist or not can be easilyconfirmed even by visual observation by performing etching such as Seccoetching, or Cu decoration to visualize them. When a silicon waferincluding dislocation clusters is employed, a large amount of defects(such as stacking faults) induced by the dislocation clusters wouldoccur; therefore, such a silicon wafer cannot be used as a substrate ofan epitaxial silicon wafer.

When the above single crystal silicon ingot is grown, if the oxygenconcentration is too high, epitaxial defects are easily formed by oxygenprecipitates. Further, in the case of using a wafer collected from acrystalline region including the OSF latent nucleus region 42, epitaxialdefects (stacking fault) may be formed in the epitaxial layer formed onthe wafer. In order to reduce such defects, the oxygen concentration iseffectively lowered, specifically, it is preferable to lower the oxygenconcentration to 16×10¹⁷ atoms/cm³ or less (ASTM F121-1979). In terms ofensuring the strength of the wafer, the oxygen concentration ispreferably 6×10¹⁷ atoms/cm³ or more.

The polarity of the thus prepared silicon wafer 10 may be n-type orp-type. In addition to the irradiation with cluster ions describedbelow, a silicon wafer having a crystal into which carbon and/ornitrogen are added may be used to further increase gettering capability.

Next, the technical meaning of employing the step of cluster ionirradiation, which is a characteristic step of the present invention,will be described with its operation and effect. The modifying layer 18formed as a result of irradiation with the cluster ions 16 is a regionwhere the constituent element of the cluster ions 16 is localized atcrystal interstitial positions or substitution positions in the crystallattice of the surface portion 10A of the silicon wafer 10, which regionfunctions as a gettering site. The reason may be as follows. Afterirradiation in the form of cluster ions, elements such as carbon andboron are localized at high density at substitution positions andinterstitial positions in the single crystal silicon. It has beenexperimentally found that when carbon or boron is turned into a solidsolution to the equilibrium concentration of single crystal silicon orhigher, the solid solubility of heavy metals (saturation solubility oftransition metal) extremely increases. It is considered that carbon orboron made into a solid solution to the equilibrium concentration orhigher increases the solubility of heavy metals, which results insignificantly increased rate of trapping the heavy metals.

Here, since irradiation with the cluster ions 16 is performed in thepresent invention, higher gettering capability can be achieved ascompared to cases of implanting monomer ions. Moreover, recovery heattreatment can be omitted. Therefore, the epitaxial silicon wafer 100achieving higher gettering capability can be more efficiently produced,and white spot defects are expected to be reduced more than conventionalin back-illuminated solid-state image sensing devices produced from theepitaxial silicon wafer 100 obtained by the producing methods.

Further, as described above, a silicon wafer free of dislocationclusters and COPs is used as the silicon wafer 10 in the presentinvention. However, this wafer may have one or more of the OSF latentnucleus region 42, the Pv(1) region 43, the Pv(2) region 44, and the Piregion 45. In that case, the oxygen precipitate density in the waferdiameter direction is not uniform in the wafer surface portion, so thatthe gettering capability varies in the diameter direction. However,since the modifying layer 18 formed by irradiation with cluster ionshave high gettering capability, the gettering capability in the vicinityof the wafer surface can be uniform in the wafer surface portion. Notethat “cluster ions” herein mean clusters formed by aggregation of aplurality of atoms or molecules, which are ionized by being positivelyor negatively charged. A cluster is a bulk aggregate having a plurality(typically about 2 to 2000) of atoms or molecules bound together.

The inventor of the present invention considers the operation achievingsuch an effect as follows.

For example, when carbon monomer ions are implanted into a siliconwafer, the monomer ions sputter silicon atoms forming the silicon waferto be implanted to a predetermined depth position in the silicon wafer,as shown in FIG. 3B. The implantation depth depends on the kind of theconstituent element of the implantation ions and the accelerationvoltage of the ions. In this case, the concentration profile of carbonin the depth direction of the silicon wafer is relatively broad, and thecarbon implanted region extends approximately 0.5 mm to 1 mm. When aplurality of species of ions are simultaneously implanted at the sameenergy, lighter elements are implanted more deeply, in other words,elements are implanted at different positions depending on their masses.Accordingly, the concentration profile of the implanted elements isbroader in such a case.

Monomer ions are typically implanted at an acceleration voltage of about150 keV to 2000 keV. However, the ions collide with silicon atoms withthe energy, which results in disrupted crystallinity of the surfaceportion of the silicon wafer, to which the monomer ions are implanted.Accordingly, the crystallinity of an epitaxial layer to be grown lateron the wafer surface is disrupted. Further, the higher the accelerationvoltage is, the more the crystallinity is disrupted. Therefore, it isrequired to perform heat treatment for recovering the crystallinityhaving been disrupted at a high temperature for a long time after ionimplantation (recovery heat treatment).

On the other hand, when cluster ions formed from, for example, a siliconwafer is irradiated with carbon and boron as shown in FIG. 3A, thecluster ions 16 are instantaneously turned into a high temperature stateof about 1350° C. to 1400° C. due to the irradiated energy, thus meltingsilicon. After that, the silicon is rapidly cooled to form solidsolutions of carbon and boron in the vicinity of the surface of thesilicon wafer. Accordingly, a “modifying layer” herein means a layer inwhich the constituent element of the ions used for irradiation forms asolid solution at crystal interstitial positions or substitutionpositions in the crystal lattice of the surface portion of the siliconwafer. The concentration profile of carbon and boron in the depthdirection of the silicon wafer is sharper as compared with the case ofmonomer ions, although depending on the acceleration voltage and thecluster size of the cluster ions. The thickness of the region locallyirradiated with carbon and boron (that is, the modification layer) isabout 500 nm or less (for example, about 50 nm to 400 nm). Afterirradiation in the form of cluster ions, the elements are thermallydiffused to some extent in the process of forming the epitaxial layer20. Accordingly, in the concentration profile of carbon and boron afterthe formation of the epitaxial layer 20, broad diffusion regions areprovided on both sides of the peak where these elements are localized.However, the thickness of the modifying layer does not vary greatly (seeFIG. 7A described below). Consequently, carbon and boron areprecipitated at a high concentration in a localized region. Since themodifying layer 18 is formed in the vicinity of the surface of thesilicon wafer, further proximity gettering can be performed. This isconsidered to result in achievement of still higher getteringcapability. The irradiation can be performed simultaneously with aplurality of species of ions in the form of cluster ions

In general, irradiation with cluster ions is performed at anacceleration voltage of about 10 keV/Cluster to 100 keV/Cluster.However, since a cluster is an aggregate of a plurality of atoms ormolecules, the irradiation with the ions can be performed at reducedenergy per one atom or one molecule, which reduces damage to thecrystals in the silicon wafer. Further, cluster ion irradiation does notdisrupt the crystallinity of a silicon wafer as compared withmonomer-ion implantation also due to the above described implantationmechanism. Accordingly, after the first step, without performingrecovery heat treatment on the silicon wafer 10, the silicon wafer 10can be transferred into an epitaxial growth apparatus to be subjected tothe second step.

The cluster ions 16 may include a variety of clusters depending on thebinding mode, and can be generated, for example, by known methodsdescribed in the following documents. Methods of generating gas clusterbeam are described in (1) JP 09-041138 A and (2) JP 04-354865 A. Methodsof generating ion beam are described in (1) Junzo Ishikawa, “Chargedparticle beam engineering”, ISBN 978-4-339-00734-3 CORONA PUBLISHING,(2) The Institution of Electrical Engineers of Japan, “Electron/Ion BeamEngineering”, Ohmsha, ISBN 4-88686-217-9, and (3) “Cluster IonBeam-Basic and Applications”, THE NIKKAN KOGYO SHIMBUN, ISBN4-526-05765-7. In general, a Nielsen ion source or a Kaufman ion sourceis used for generating positively charged cluster ions, whereas a highcurrent negative ion source using volume production is used forgenerating negatively charged cluster ions.

The conditions for irradiation with cluster ions will be describedbelow. First, examples of the element used for irradiation include, butnot limited to, carbon, boron, phosphorus, and arsenic. In terms ofachieving higher gettering capability, the cluster ions preferablycontain carbon as a constituent element. Carbon atoms at a lattice sitehave a smaller covalent radius than a single crystal silicon ingot, sothat a compression site is produced in the silicon crystal lattice,which results in high gettering capability for attracting impurities inthe lattice.

Further, the cluster ions preferably contain at least two kinds ofelements including carbon as constituent elements. Since the kinds ofmetals to be efficiently gettered depend on the kinds of theprecipitated elements, solid solutions of two or more kinds of elementscan cover a wider variety of metal contaminations. For example, carboncan efficiently getter nickel, whereas boron can efficiently gettercopper and iron.

The compounds to be ionized are not limited in particular, but examplesof compounds to be suitably ionized include ethane, methane, propane,dibenzyl (C₁₄H₁₄), and carbon dioxide (CO₂) as carbon sources, anddiborane and decaborane (B₁₀H₁₄) as boron sources. For example, when amixed gas of dibenzyl and decaborane is used as a material gas, ahydrogen compound cluster in which carbon, boron, and hydrogen areaggregated can be produced. Alternatively, when cyclohexane (C₆H₁₂) isused as a material gas, cluster ions formed from carbon and hydrogen canbe produced. Further, as a carbon source compound, clusters C_(n)H_(m)(3≦n≦16, 3≦m≦10) generated from pyrene (C₁₆H₁₀), dibenzyl (C₁₄H₁₄), orthe like is preferably used in particular. This facilitates theformation of beams of small-sized cluster ions having a small diameter.

Next, the acceleration voltage and the cluster size of the cluster ionsare controlled, thereby controlling the peak position of theconcentration profile of the constituent elements in the depth directionof the modifying layer 18. “Cluster size” herein means the number ofatoms or molecules constituting one cluster.

In the first step of the present invention, in terms of achieving highergettering capability, the irradiation with the cluster ions 16 ispreferably performed such that the peak of the concentration profile ofthe constituent elements in the depth direction of the modifying layer18 lies at a depth within 150 nm from the surface portion 10A of thesilicon wafer 10. Note that herein “the concentration profile of theconstituent elements in the depth direction” in the case where theconstituent elements include at least two kinds of elements, means theprofiles with respect to the respective single element but not withrespect to the total thereof.

For a condition required to set the peak positions to the depth level,when C_(n)H_(m) (3≦n≦16, 3≦m≦10) is used for the cluster ions 16, theacceleration voltage per one carbon atom is higher than 0 keV/atom and50 keV/atom or lower, preferably 40 keV/atom or lower. Further, thecluster size is 2 to 100, preferably 60 or less, more preferably 50 orless.

In addition, for adjusting the acceleration voltage, two methods of (1)electrostatic field acceleration and (2) oscillating field accelerationare commonly used. The former method includes a method in which aplurality of electrodes are arranged at regular intervals, and the samevoltage is applied therebetween, thereby forming constant accelerationfields in the direction of the axes. The latter method includes a linearacceleration (linac) method in which ions are transferred along astraight line and accelerated with high-frequency waves. The clustersize can be adjusted by controlling the pressure of gas ejected from anozzle, the pressure of vacuum vessel, the voltage applied to thefilament in the ionization, and the like. The cluster size is determinedby finding the cluster number distribution by mass spectrometry usingthe oscillating quadrupole field or by time-of-flight mass spectrometry,and finding the mean value of the cluster numbers.

The cluster dose can be adjusted by controlling the ion irradiationtime. In the present invention, the dose of carbon is 1×10¹³ atoms/cm²or more and 1×10¹⁶ atoms/cm² or less. A dose of less than 1×10¹³atoms/cm² would lead to insufficient gettering capability, whereas adose exceeding 1×10¹⁶ atoms/cm² would cause great damage to theepitaxial surface. The cluster dose is preferably 1×10¹⁴ atoms/cm² ormore and 5×10¹⁵ atoms/cm² or less.

According to the present invention, as described above, it is notrequired to perform recovery heat treatment using a rapidheating/cooling apparatus or the like separate from the epitaxialapparatus, such as an RTA or an RTO. This is because the crystallinityof the silicon wafer 10 can be sufficiently recovered by hydrogen bakingperformed prior to epitaxial growth in an epitaxial apparatus forforming the epitaxial layer 20 to be described below. For typicalconditions for hydrogen baking, the epitaxial growth apparatus has ahydrogen atmosphere inside and the silicon wafer 10 is introduced intothe furnace at a furnace temperature of 600° C. to 900° C. and it isheated to a temperature in the range of about 1100° C. to 1200° C. at arate of 1° C./s to 15° C./s, and the temperature is kept for 30 s to 1min. This hydrogen baking is conventionally performed for removing anatural oxide film formed on a wafer surface due to the cleaning priorto the growth of the epitaxial layer. However, hydrogen baking under theabove conditions can sufficiently recover the crystallinity of thesilicon wafer 10.

Needless to say, the recovery heat treatment may be performed using aheating apparatus separate from the epitaxial apparatus after the firststep prior to the second step. This recovery heat treatment may beperformed at 900° C. to 1200° C. for 10 s to 1 h. Here, the bakingtemperature is 900° C. to 1200° C. At a temperature lower than 900° C.,it is difficult to achieve the effect of recovering the crystallinity,whereas at a temperature of higher than 1200° C., slips would occur dueto the high temperature heat treatment, which increases the heat load onthe apparatus. Further, the heat processing time is 10 s to 1 h or less.It is difficult to achieve the effect of recovery in cases of less than10 s, whereas the productivity is deteriorated in cases of more than 1h, which increases the heat load on the apparatus.

Such recovery heat treatment can be performed using, for example, arapid heating/cooling apparatus such as an RTA or an RTO, or a batchtype heating apparatus (vertical type heating apparatus, horizontal typeheating apparatus). The former apparatus is not suitable for long-timetreatment, since it performs heating by lamp illumination, and issuitable for heat treatment for within 15 min. On the other hand, thelatter can be used for simultaneously heating a multiplicity of wafersat a time, although it takes a long time to raise the temperature to apredetermined temperature. Further, the latter performs resistanceheating, which can be used for long-time heat treatment. The heatingapparatus to be used may be selected as appropriate in consideration ofthe conditions for irradiation with the cluster ions 16.

A silicon epitaxial layer can be given as an example of the epitaxiallayer 20 formed on the modifying layer 18, and the silicon epitaxiallayer can be formed under typical conditions. For example, a source gassuch as dichlorosilane or trichlorosilane can be introduced into achamber using hydrogen as a carrier gas, so that the source material canbe epitaxially grown on the silicon wafer 10 by CVD at a temperature inthe range of about 1000° C. to 1200° C., although the growth temperaturevaries depending on the source gas to be used. The thickness of theepitaxial layer 20 is preferably in the range of 1 μm to 15 μm. When thethickness is less than 1 μm, the resistivity of the epitaxial layer 20would change due to outdiffusion of dopants from the silicon wafer 10,whereas a thickness exceeding 15 μm would affect the spectralsensitivity characteristics of the solid-state image sensing device. Theepitaxial layer 20 is used as a device layer for producing aback-illuminated solid-state image sensing device.

Next, a silicon wafer 100 produced according to the above methods willbe described. As shown in FIG. 1C, this epitaxial silicon wafer 100includes a silicon wafer 10; a modifying layer 18 formed from a certainelement in a surface portion of the silicon wafer 10; and an epitaxiallayer 20 on the modifying layer 18. Here, the silicon wafer 10 is asilicon wafer free of dislocation clusters and COPs, and the full widthhalf maximum W of the concentration profile of the certain element inthe depth direction of the modifying layer 18 is 100 nm or less.Specifically, according to the method of producing an epitaxial wafer,of the present invention, the element constituting cluster ions can beprecipitated at a high concentration in a localized region as comparedwith monomer-ion implantation, which results in the full width halfmaximum W of 100 nm or less. The lower limit of the full width halfmaximum can be set to 10 nm.

Note that “concentration profile in the depth direction” herein means aconcentration distribution in the depth direction, which is measured bysecondary ion mass spectrometry (SIMS). Meanwhile, “full width halfmaximum of the concentration profile of a certain element in the depthdirection” means a full width half maximum of the concentration profileof a certain element in an epitaxial layer measured by SIMS and if thethickness of the epitaxial layer exceeds 1 μm, the epitaxial layer ispreviously thinned to 1 μm considering the measurement precision.

The certain element is not limited in particular as long as it is anelement other than silicon. However, carbon or at least two kinds ofelements containing carbon are preferable as described above.

In terms of achieving higher gettering capability, it is preferable thatthe peak of the concentration profile of the constituent element in thedepth direction of the modifying layer 18 lies at a depth within 150 nmfrom the surface of the silicon wafer 10 in the epitaxial silicon wafer100. Further, the peak concentration of the concentration profile ispreferably 1×10¹⁵ atoms/cm³ or more, more preferably in the range of1×10¹⁷ atoms/cm³ to 1×10²² atoms/cm³, and still more preferably in therange of 1×10¹⁹ atoms/cm³ to 1×10²¹ atoms/cm³.

The thickness of the modifying layer 18 in the thickness direction maybe approximately in the range of 30 nm to 400 nm.

The metal contamination of the epitaxial silicon wafer 100 of thepresent invention can be further suppressed by achieving highergettering capability than conventional. Moreover, since a silicon waferfree of dislocation clusters and COPs is used as a substrate, anepitaxial silicon wafer with epitaxial defects due to dislocationclusters and COPs being minimized can be obtained.

In a method of producing a solid-state image sensing device according toan embodiment of the present invention, a solid-state image sensingdevice is formed on the epitaxial layer 20 disposed on the surface ofthe epitaxial silicon wafer produced by the above method or the abovedescribed epitaxial silicon wafer, that is, the epitaxial silicon wafer100. In solid-state image sensing devices obtained by this producingmethod, formation of white spot defects can be sufficiently suppressedthan conventional.

Representative embodiments of the present invention have been describedabove. However, the present invention is not limited to thoseembodiments. For example, two epitaxial layers may be formed on thesilicon wafer 10.

EXAMPLES

FIG. 4 is a diagram schematically illustrating the structure of a singlecrystal production apparatus used to achieve the conditions forproducing a single crystal silicon ingot which is the material for asilicon wafer free of dislocation clusters and COPs that is used as asubstrate of an epitaxial silicon wafer of the present invention. Asshown in this diagram, the enclosure of the single crystal productionapparatus 50 is constituted by a chamber 51, and a crucible 52 isdisposed in a center part of the chamber. The crucible 52 has a doublelayer structure composed of an inner quartz crucible 52 a and an outergraphite crucible 52 b, which is fixed to the tip of a cruciblerotating/elevating shaft 53 capable of rotation and elevation.

A resistance heating heater 54 surrounding the crucible 52 is disposedon the outer side of the crucible 52, and a thermal insulator 60 isprovided on the outer side of the resistance heating heater 54 along theinner surface of the chamber 51. A lifting shaft 55 such as a wirerotating at a predetermined speed in the same direction as or oppositeto the coaxial crucible rotating/elevating shaft 53, is provided abovethe crucible 52. A seed crystal S is held by a seed crystal holder 56attached to the lower end of the lifting shaft 55.

A cylindrical heat shield 59 surrounding a growing ingot I is disposedin an upper part of the crucible 52 in the chamber 51. The heat shield59 shields the growing ingot I against high temperature radiant heatfrom material melt M in the crucible 52 and the side walls of the heater54 and the crucible 52, thereby adjusting the amount of incident lightand the amount of heat diffused in the vicinity of the crystal growthinterface. The heat shield 59 serves to control the temperature gradientin the direction of the pulling axis at the center of the single crystalingot and the edge of the single crystal ingot.

A gas inlet 57 for introducing an inert gas such as Ar gas into thechamber 51 is provided on an upper portion of the chamber 51. An exhaustport 58 for evacuating the chamber 51 by the action of a vacuum pump notshown is provided at a lower portion of the chamber 51. The inert gasintroduced through the gas inlet 57 into the chamber 51 flows downbetween the growing silicon single crystal ingot I and the heat shield59, passes through the gap between the bottom of the heat shield 59 andthe liquid surface of the material melt M, flows out of the heat shield59 and then toward the out of the crucible 52, and subsequently flowsdown outside the crucible 52 to be discharged from the exhaust port 58.

Using this single crystal production apparatus 50, a solid material suchas polycrystalline silicon filling the inside of the crucible 52 ismelted by heating with the heater 54, with the chamber 51 being kept inan Ar gas atmosphere under reduced pressure, thereby forming thematerial melt M. After that, the lifting shaft 55 is lowered to immersethe seed crystal S in the material melt M, and raising the lifting shaft55 upward while rotating the crucible 52 and the lifting shaft 55 in acertain direction, thereby growing the ingot I downward from the seedcrystal S.

In this example, in order to grow a single crystal ingot constituted bya denuded zone uniform in the diameter direction, a single crystal ingotI was grown as follows such that the relationship between thetemperature gradient Gc of the center portion of the single crystalingot in the pulling axis direction and the temperature gradient Ge atthe edge of the single crystal ingot satisfies a condition of Gc/Ge>1 attemperatures of the growing single crystal ingot in the range of themelting point to 1300° C. The condition was satisfied by adjusting thesize, shape, and the installation height of the heat shield 59, andvarying the pulling speed from high speed (1.0 mm/min) to low speed (0.3mm/min), thereby growing a straight body having a crystalline regionprofile varying in the length direction. The grown single crystalsilicon ingot I is an n-type single crystal silicon ingot having acrystal orientation of <100> and a straight body diameter of 310 mm,doped with phosphorus (1×10¹⁵ atoms/cm³ to 1×10¹⁷ atoms/cm³), and theoxygen concentration of the ingot I (ASTM F121-1979) is 12×10¹⁷atoms/cm³ to 14×10¹⁷ atoms/cm³.

The distribution of defects formed in the single crystal silicon ingotgrown as described above was evaluated. Specifically, first, the singlecrystal silicon ingot grown in the experiment of changing the pullingspeed was vertically divided along the lifting shaft to prepare platesamples, and the prepared samples, were then subjected to oxygenprecipitation heat treatment (nitrogen atmosphere, 800° C.×4 h+1000°C.×16 h). Subsequently, the heat-treated sample was dipped in a coppersulfate aqueous solution to be decorated with Cu, and then subjected toheat treatment in a nitrogen atmosphere at 900° C. for 20 min. Afterthat, the distribution of defects in the surface of the sample wasevaluated by X-ray topography. The schematic diagram of the obtaineddefect distribution is shown in FIG. 5.

The pulling condition (pulling speed) was changed to obtain crystallineregions at the positions of lines (a) to (d) in FIG. 5. Four levels ofsingle crystal silicon ingots (a) to (d) having crystalline regionscorresponding to the respective positions of the lines (a) to (d) havingdifferent crystalline region distributions were grown. All theconditions other than the changed pulling speed are the same as thegrowing conditions in the experiment of changing the pulling speed.

The four levels of grown single crystal silicon ingots were subjected toprocess steps of known peripheral grinding, slicing, lapping, etching,and mirror polishing, thereby preparing silicon wafers having athickness of 725 μm. Specifically, four kinds of wafers having thefollowing crystalline regions were prepared.

Whether or not dislocation clusters are contained in the preparedsilicon wafers was examined by visual inspection after Secco etching;however, no dislocation clusters were found in any of the siliconwafers.

Wafer (a): COP formation region constitutes the entire surface of wafer

Wafer (b): Mixed region of OSF latent nucleus region and Pv(1) region

Wafer (c): Mixed region of OSF latent nucleus region and Pv(2) region

Wafer (d): Mixed region of Pv(2) region and Pi region

Invention Example 1

Using the wafer (b) fabricated as described above, using a cluster iongenerator (CLARIS produced by Nissin Ion Equipment Co., Ltd.), C₅H₅clusters were generated as cluster ions, and the silicon wafer wasirradiated with the cluster ions under the conditions of dose: 9.00×10¹³Clusters/cm² (carbon dose: 4.50×10¹⁴ atoms/cm²), and accelerationvoltage per one carbon atom: 14.8 keV/atom. Subsequently, the siliconwafer was cleaned with HF and then transferred into a single waferprocessing epitaxial growth apparatus (produced by Applied Materials,Inc.) and subjected to hydrogen baking at 1120° C. for 30 s in theapparatus. A silicon epitaxial layer (thickness: 8 μm, kind of dopant:phosphorus, dopant concentration: 1×10¹⁵ atoms/cm³) was then epitaxiallygrown on the silicon wafer by CVD at 1150° C. using hydrogen as acarrier gas and trichlorosilane as a source gas, thereby obtaining asilicon epitaxial wafer of the present invention.

Invention Examples 2 and 3

Epitaxial silicon wafers according to the present invention wereproduced in the same manner as in Invention Example 1, except that thesilicon wafer as a substrate was changed to the wafer (c) (InventionExample 2) and the wafer (d) (Invention Example 3). Note that inInvention Examples 1 to 3, irradiation with cluster ions was performedat 80 keV/Cluster, and each cluster was composed of five carbon atoms(atomic weight 12) and five hydrogen atoms (atomic weight 1).Accordingly, the energy received by one carbon atom was80×{12×5/(12×5+1×5)}/5˜14.8 keV.

Comparative Examples 1 to 3

Epitaxial silicon wafers according to Comparative Examples 1 to 3 wereproduced in the same manner as in Invention Examples 1 to 3 except thatmonomer ions of carbon were produced using CO₂ as a material gas and amonomer-ion implantation step was performed under the conditions ofdose: 9.00×10¹³ atoms/cm² and acceleration voltage: 300 keV/atom insteadof the step of irradiation with cluster ions. Specifically, wafers (b)to (d) were used as substrates in Comparative Examples 1 to 3,respectively, and carbon monomer ions were implanted into the siliconwafers at an acceleration voltage of 300 keV.

Comparative Example 4

An epitaxial silicon wafer according to Comparative Example 4 wasproduced in the same manner as in Invention Example 1, except that thesilicon wafer was changed to the wafer (a).

Comparative Example 5

An epitaxial silicon wafer according to Comparative Example 5 wasproduced in the same manner as in Comparative Example 1, except that thesilicon wafer was changed to the wafer (a).

The samples prepared in Invention Examples and Comparative Examplesabove were evaluated. The evaluation methods are shown below.

(1) SIMS Measurement

In order to explain the difference of carbon distribution betweenimmediately after irradiation with cluster ions and immediately afterimplantation of monomer ions, first, SIMS measurement was performed onthe silicon wafers of Invention Example 3 and Comparative Example 3before forming the epitaxial layers. The obtained carbon concentrationprofile is shown in FIG. 6 for reference. Here, the horizontal axis inFIG. 6 corresponds to the depth from the surface of the silicon wafer.

Next, SIMS measurement was performed on the epitaxial silicon wafers ofInvention Example 3 and Comparative Example 3. The obtained carbonconcentration profiles are shown in FIGS. 7A and 7B. The horizontal axisin each of FIGS. 7A and 7B corresponds to the depth from the surface ofthe epitaxial silicon wafer.

Further, SIMS measurement was performed on the samples prepared inInvention Examples and Comparative Examples after reducing the thicknessof the epitaxial layers to 1 μm. The half widths of the measured carbonconcentration profiles are shown in Table 1. Note that as describedabove, the half widths shown in Table 1 are half widths measured by SIMSmeasurement after reducing the thickness of the epitaxial layers to 1μm, so that the half widths shown in Table 1 are different from the halfwidths shown in FIGS. 7A and 7B. Further, the peak position of theconcentration and the peak concentration at the time of the SIMSmeasurement on each sample with the thinned epitaxial wafer are alsoshown in Table 1.

TABLE 1 Cluster ion irradiation conditions (Invention Example)Evaluation result Monomer-ion implantation conditions SIMS measurementresult (Comparative Example) Carbon Irradiation/ Acceleration Doseconcentration Carbon peak Gettering implantation voltage (Clusters/cm²)Wafer peak position concentartion Half width capability Stacking faultsions (keV/atom) (atoms/cm²) type (nm) (atoms/cm³) (nm) evaluation(number/wafer) Invention C₅H₅ 14.8 9.00 × 10¹³ (b) 50.1 3.00 × 10¹⁹ 70.5A 0 Example 1 Pv(1) + OSF Invention C₅H₅ 14.8 9.00 × 10¹³ (c) 50.3 3.03× 10¹⁹ 70.3 A 0 Example 2 OSF + Pv(2) Invention C₅H₅ 14.8 9.00 × 10¹³(d) 50.3 2.98 × 10¹⁹ 70.4 A 0 Example 3 Pv(2) + Pi Comparative CO₂ 3009.00 × 10¹³ (b) 380 9.00 × 10¹⁸ 245.8 C 0 Example 1 Pv(1) + OSFComparative CO₂ 300 9.00 × 10¹³ (c) 380.2 9.00 × 10¹⁸ 245.6 C 0 Example2 OSF + Pv(2) Comparative CO₂ 300 9.00 × 10¹³ (d) 380.1 9.00 × 10¹⁸245.7 C 0 Example 3 Pv(2) + Pi Comparative C₅H₅ 14.8 9.00 × 10¹³ (a)50.2 3.00 × 10¹⁹ 70.4 A 2 Example 4 COP Comparative CO₂ 300 9.00 × 10¹³(a) 380.1 9.03 × 10¹⁸ 246 C 3 Example 5 COP

(2) Evaluation of Gettering Capability

The silicon wafer surface of each sample fabricated in InventionExamples and Comparative Examples was contaminated on purpose by a spincoat contamination method using Ni contaminant liquid (1.0×10¹²atoms/cm²) and was then subjected to heat treatment at 900° C. for 30min. After that, a SIMS measurement was performed. The Ni concentrationprofiles and the carbon concentration profiles of Invention Example 3and Comparative Example 3 are shown as representative measurementresults (FIGS. 7A and 7B). Results of gettering capability evaluationwith respect to other invention examples and comparative examples areshown in Table 1. Note that the criteria were classified as followsdepending on the value of the peak concentration of the Ni concentrationprofile.

A: (Excellent) 1.0×10¹⁷ atoms/cm³ or more

B: (Good) 5.0×10¹⁶ atoms/cm³ or more and less than 1.0×10¹⁷ atoms/cm³

C: (Fair) 1.0×10¹⁶ atoms/cm³ or more and less than 5.0×10¹⁶ atoms/cm³

(3) Evaluation of Epitaxial Defects

The surface of the epitaxial wafer of each of the samples fabricated ininvention Examples and Comparative Examples was observed and evaluatedusing Surfscan SP2 manufactured by KLA-Tencor Corporation to examine theformation of LPDs. The observation was performed using an observationmode of oblique mode (oblique incidence mode), and the surface pits wereexamined based on the ratio of the sizes measured using wide/narrowchannels. Subsequently, whether the LPDs were stacking faults (SFs) ornot was evaluated using a scanning electron microscope (SEM) byobserving and evaluating the area where the LPDs are formed. After that,samples for observing and evaluating cross sections including the SFformation area were fabricated by focused ion beam (FIB) processing.Finally, these evaluation samples were observed and evaluated using atransmission electron microscope (TEM), thereby evaluating whether theLPDs were SFs caused by COPs or not. The number of SFs is shown in Table1.

First, Invention Example 3 is compared with Comparative Example 3 whichis different only in that monomer ion implantation was performed insteadof irradiation with cluster ions. As shown in FIG. 6, comparing thecarbon concentration profiles of silicon wafers before forming anepitaxial layer, which silicon wafers are in-process products, betweenimmediately after irradiation with cluster ions and immediately aftermonomer-ion implantation, the carbon concentration after the irradiationwith cluster ions is sharp, whereas the carbon concentration profileafter monomer-ion implantation is broad. This suggests that the tendencyof the carbon concentration profile remains the same even after formingthe epitaxial layer. Actually, as evident from the carbon concentrationprofiles of these in-process products provided with an epitaxial layer(FIGS. 7A and 7B), the irradiation with cluster ions yielded a modifyinglayer more locally at a higher concentration than in monomer-ionimplantation. Further, comparing Invention Example 3 and ComparativeExample 3 based on the Ni concentration profiles shown in FIGS. 7A and7B, the modifying layer of Invention Example 3 formed by cluster ionirradiation is found to have captured a large amount of Ni, thusachieving high gettering capability.

Moreover, as shown in Table 1, in each of Invention Examples 1 to 3 andComparative Example 4 in which irradiation with cluster ions wasperformed, the half width was 100 nm or less, and sufficient getteringcapability was achieved. On the other hand, in Comparative Examples 1 to3 and 5 in which monomer-ion implantation was performed, the half widthexceeded 100 nm, so that poor gettering capability was achieved. Thus,in Invention Examples 1 to 3 and Comparative Examples 1 to 3 and 5, inwhich irradiation with cluster ions was performed, higher getteringcapability can be achieved due to smaller half width of the carbonconcentration profile than in Comparative Example 4 in which monomer-ionimplantation was performed.

In each of Invention Examples 1 to 3 and Comparative Examples 1 to 3using the wafers (b) to (d), the number of SFs was zero, whereas SFswere found in Comparative Examples 4 and 5 using the wafer (a) collectedfrom the COP formation region. Thus, it is shown that epitaxial defectscan be prevented by using the wafers (b) to (d).

INDUSTRIAL APPLICABILITY

According to the present invention, an epitaxial silicon wafer which cansuppress metal contamination by achieving higher gettering capability,which has minimized epitaxial defects caused by dislocation clusters andCOPs, can be efficiently produced. Therefore, the present invention isuseful in an industry of semiconductor epitaxial wafer production.

REFERENCE NUMERALS

-   100: Epitaxial silicon wafer-   10: Silicon wafer-   10A: Surface portion of silicon wafer-   16: Cluster ions-   18: Modifying layer-   20: Epitaxial layer-   41: COP formation region-   42: OSF latent nucleus region-   43: Oxygen precipitation promoted region (Pv(1) region)-   44: Oxygen precipitation promoted region (Pv(2) region)-   45: Oxygen precipitation inhibited region (Pi region)-   46: Dislocation cluster region-   50: Single crystal production apparatus-   51: Chamber-   52: Crucible-   52 a: Quartz crucible-   52 b: Graphite crucible-   53: Crucible rotating/elevating shaft-   54: Heater-   55: Lifting shaft-   56: Seed crystal holder-   57: Gas inlet-   58: Exhaust port-   59: Heat shield-   60: Thermal insulator-   I: Single crystal silicon ingot-   S: Seed crystal-   M: Material melt

The invention claimed is:
 1. A method of producing an epitaxial siliconwafer, comprising: a first step of irradiating a silicon wafer free ofdislocation clusters and COPs with cluster ions including a constituentelement contributing to gettering of heavy metal to form a modifyinglayer formed from the constituent element of the cluster ions in asurface portion of the silicon wafer, a second step of forming anepitaxial layer on the modifying layer of the silicon wafer, wherein, inthe first step, the silicon wafer is irradiated with the cluster ionssuch that the full width half maximum of a concentration profile of theconstituent element in the depth direction of the modifying later afterthe second step is 100 nm or less.
 2. The method of producing anepitaxial silicon wafer according to claim 1, wherein the cluster ionscontain carbon as a constituent element.
 3. The method of producing anepitaxial silicon wafer according to claim 2, wherein the cluster ionscontain at least two kinds of elements including carbon as constituentelements.
 4. The method of producing an epitaxial silicon waferaccording to claim 1, wherein, after the first step, the silicon waferis transferred into an epitaxial growth apparatus to be subjected to thesecond step without heat treating the silicon wafer for recovering itscrystallinity.
 5. The method of producing an epitaxial silicon waferaccording to claim 1, wherein, in the first step, the silicon wafer isirradiated with the cluster ions such that the peak of a concentrationprofile of the constituent element in the depth direction of themodifying layer lies at a depth within 150 nm from the surface of thesilicon wafer.
 6. The method of producing an epitaxial silicon waferaccording to claim 5, wherein the first step is performed under theconditions of acceleration voltage per one carbon atom: 50 keV/atom orless, cluster size: 100 or less, and carbon dose: 1×10¹⁶ atoms/cm² orless.
 7. The method of producing an epitaxial silicon wafer according toclaim 5, wherein the first step is performed under the conditions of:acceleration voltage per one carbon atom: 40 keV/atom or less, clustersize: 60 or less, and carbon dose: 5×10¹⁵ atoms/cm² or less.
 8. A methodof producing a solid-state image sensing device, wherein a solid-stateimage sensing device is formed on the epitaxial silicon layer, locatedin the surface portion of the epitaxial wafer fabricated by theproducing method according to claim 1.